1. Field of the Invention
The present invention relates to a power management apparatus, a power management method, and a power management system, in particular, a power management apparatus, a power management method, and a power management system, which are used in a vehicle including a plurality of electric power storage devices and a power converter.
2. Description of the Related Art
Against the background of greenhouse effect gas issues of the earth, a technology of reducing a fuel consumption of an automobile is desired to be developed. Under such circumstances, a technology of recovering kinetic energy generated at the time of deceleration as power and reducing the amount of power generation at the time other than the deceleration so as to reduce a fuel consumption of a vehicle has been developed. If a voltage of a power generator is increased in the vehicle as described above, the generated power can be more efficiently stored. Therefore, power can be generated and stored at a voltage higher than a voltage region in which electric apparatuses of an engine are operated. Moreover, if power at a pressure lowered with use of a power converter is supplied to the electric apparatuses and a battery, the power can be efficiently used. In the system described above, however, if a failure occurs in the power converter, power cannot be supplied from a high-voltage circuit to a low-voltage circuit. Therefore, the power is supplied to the electric apparatuses only from the battery. When the amount of charge of the battery decreases, the electric apparatuses do not operate. In the worst cases, the vehicle cannot run.
As a conventional power management device for a vehicle, a system including two power converters in preparation for a failure of any one of the power converters has been proposed (for example, Japanese Patent Application Laid-open No. Hei 11-122701 (page 5, FIG. 1)).
A system for reducing the amount of power generated by the power generator so that an output voltage becomes approximately equal to that of the low-voltage circuit and supplying power to the low-voltage circuit when a short-circuit fault occurs between the high-voltage circuit and the low-voltage circuit has been proposed (for example, Japanese Patent No. 4143267 (page 5, FIG. 1)).
The conventional power management apparatus described in Japanese Patent Application Laid-open No. Hei 11-122701 has a configuration in which the two power converters are connected in parallel in preparation for a failure of any one of the power converters. Therefore, cost is remarkably increased with the dual-system configuration. In addition, there arises a problem of increased size.
Further, the another conventional power management device described in Japanese Patent No. 4143267 reduces the amount of power generated by the power generator so that the output voltage becomes approximately equal to that of the low-voltage circuit and performs control so that the power is supplied to the low-voltage circuit when the short-circuit fault occurs between the high-voltage circuit and the low-voltage circuit. In the case of a general failure with which the high-voltage circuit and the low-voltage circuit are not short-circuited by the power converter, however, a problem of the stop of power supply to the low-voltage remains unsolved.